The present invention relates generally to multi-engine rotary-wing aircraft, and more specifically, to modules and methods for biasing power to a multi-engine power plant, e.g., for conducting one engine inoperative (OEI) and weight bias flight procedures training therefor.
Many rotary-wing aircraft operate with a multi-engine powerplant system which provides sufficient power to facilitate continued flight operations in safety even in the event of a one engine inoperative (OEI) condition. Although an OEI condition is statistically a low-occurrence event, OEI training is employed to facilitate aircrew proficiency in the execution of power limited procedures when high fidelity simulators are not available such as when military aircrews are forward deployed.
One current commercial dual engine OEI training system simulates a higher aircraft gross weight by applying a fixed bias to depress one engine and artificially limit power available. The fixed bias increases proportional to load demand so as to allow an aircrew to safely enter into the OEI portion of training without exceeding actual engine parameters that may result in engine damage.
Current fixed bias commercial OEI training systems adequately simulate power limited procedures but require strict flight manual procedures so as to avoid entry into an unrecoverable rotor droop situation and/or a high sink rate descent. The fixed bias system requires an extensive preflight plan to determine the training aircraft gross weight (Training AGW) at which training can safely be performed.
Aircraft Gross Weight (AGW), ambient temperatures and pressure altitude determine the aircraft power requirements, such that at the training weight the fixed bias will either result in a small excess power margin or a deficit in excess power margin which simulates an OEI condition. A Weight, Altitude and Temperature (WAT) curve, using current ambient conditions, allows the aircrew to calculate the Training AGW during preflight planning for the given ambient conditions. This calculated Training AGW will assure an artificially biased power margin that allows for rotor droop yet will restrain the rate of descent associated with that rotor droop at a recoverable level. To confirm that the proper Training AGW is calculated and adhered to for maximum safety, the aircrew typically requires access to an aircraft flight manual. The aircrew must then burn down fuel to the Training AGW calculated during preflight.
Deployed military aircrews without such commercial OEI training systems often train for engine failures, high gross weight and/or high and hot operations through various instructor techniques. One technique is accomplished by physically retarding a Speed Control Lever (SCL) on an engine quadrant or by beeping back individual engine(s) with the ENGINE TRIM switches so that an instructor pilot can limit the actual engine power available to the pilot under instruction. Another technique is self-imposed power limiting to a given torque value to simulate a heavy condition. The self-imposed power limiting technique may be of limited training effectiveness as there is no actual aircraft response in the form of rotor droop should the self-imposed power limits be exceeded.
Although effective, such techniques also require significant preflight planning to execute. The training itself may also be limited by the chain of command, which often restricts aircrews from utilizing these training techniques in a takeoff or landing profile.
From a maintenance perspective, these current OEI training techniques may also asymmetrically load inputs to a main gear box (MGB, or Main Rotor Gearbox) with a transient torque spike when automatic kickout occurs at low rotor speed (Nr) and high power collective settings.